Cannabis activists are asking to be prosecuted for possession of the drug in an extraordinary bid to break down the laws on prohibition.

The move follows a wave of optimism in the cannabis legalisation movement, which supporters see as akin to the civil rights campaigns that led to the legalisation of homosexuality and women's right to vote.

For the first time in Britain, cannabis campaigners will stand in a general election, fielding up to 100 candidates.

The police and Crown Prosecution Service have become increasingly unwilling to prosecute for possession of cannabis. Juries now routinely acquit users who plead innocent on the grounds of medical necessity. Rather than take people to court, police are issuing cautions, which last week the Government announced would no longer mean carrying a criminal record for life.

However, activists are demanding to be prosecuted so that they can plead innocent under the new Human Rights Act, which prevents the Government from unduly interfering in the private life of an individual. There are at least half a dozen cases going through the courts where activists have refused cautions and deliberately admitted to using cannabis in order to test the Act. They are confident of victory.

Neil Morgan, a cannabis user in south Wales, is being prosecuted for possession after resisting an attempt by police to drop the case. He said: 'Going to court is a golden opportunity - it's the only way we'll change anything. We've waited a long time for this.'

The civil rights group Liberty is supporting the case of Jerry Ham, the founder of a homeless charity who is facing prosecution for possession of 3g of the drug. When he was caught by police, Mo Mowlam, the Cabinet Minister in charge of drug enforcement, who knew him through his work, phoned him to offer condolences.

Lawyers believe defeat for the Crown Prosecution Service under the Human Rights Act would unravel the drug prohibition laws. The number of CPS prosecutions for possession of cannabis has dropped dramatically, prompting campaigners to accuse it of trying to avoid defeat.

Roger Warren-Evans, a barrister on the council of Liberty, said: 'The Crown Prosecution Service know that, for any simple case, it could provoke a human rights defence. They're backpedalling so they don't get caught with a sucker punch on possession. It would unravel all the rest of the prohibition laws.'

Daniel Westlake, a 21-year-old building labourer, is thought to be the most likely to bring a change in the law. When caught with a small amount of cannabis, he refused to accept a caution and pleaded not guilty under the Human Rights Act. His case is soon to come before the Court of Appeal, which has the power to declare the Misuse of Drugs Act incompatible with the Human Rights Act.

Many police forces have effectively given up enforcing the laws on cannabis possession. Two chief constables, one acting and one retired, have called for its legalisation. A Police Federation report last year called for its decriminalisation, although the Government last week announced it would ignore its recommendations.

As a result, campaigners are becoming increasingly open about using and growing the drug. Colin Davies, founder of the Medical Marijuana Co-operative is growing plants in Manchester to supply - illegally - more than 100 people with medical conditions. He has been prosecuted three times, and the jury has acquitted him on each occasion. He is now thinking of importing the drug from mainland Europe. 'I think the juries will be just as sympathetic,' he said.

Even social users are openly challenging the police. Mark Gibson, a prospective parliamentary candidate for the Legalise Cannabis Alliance in Cumbria, and a regular user, said: 'There are many more people standing up and being counted. If the police want to arrest me they can, but they don't pay any attention to me any more.'

A cannabis rally is being organised in London in May, in full cooperation with the police. A separate march on Downing Street is being planned.

Attitudes have changed dramatically both in the UK and abroad. Last year, a third of the Shadow Cabinet admitted to having tried cannabis. Last month, Belgium legalised the drug, following a similar move by Switzerland last year. Portugal, Spain and Italy have all decriminalised possession of cannabis. Holland has officially tolerated the drug for years.

Warren-Evans says the Human Rights Act would force Britain to follow Europe: 'The cool neutrality of the courts will get the politicians off the hook. That will happen before the end of the year. The whole apparatus of prohibition will fall.'